Activating mutations in the Notch1 gene are present in >50% of human T cell-ALL (T-ALL) cases making Notch1 the most prominent oncogene, which is specifically involved in the pathogenesis of this disease, and defining T-ALL as a disease that is primarily characterized by aberrant Notch1 activation (35–38). Here, NOTCH1 is linked to acute lymphoblastic leukemia.